[PATCH v9 24/26] netfs: Check for too much data being read

[David Howells <dhowells@redhat.com>]

Put in a check in read subreq termination to detect more data being read
for a subrequest than was requested.  In the event that this happens, abort
the rest of the read request on the basis that some of the read buffer may
have been corrupted and return -EIO.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Paulo Alcantara <pc@manguebit.org>
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
---
 fs/netfs/read_collect.c      | 23 +++++++++++++++++++++++
 include/trace/events/netfs.h |  1 +
 2 files changed, 24 insertions(+)

diff --git a/fs/netfs/read_collect.c b/fs/netfs/read_collect.c
index cf7c36037edc..21eb7f74d66e 100644
--- a/fs/netfs/read_collect.c
+++ b/fs/netfs/read_collect.c
@@ -307,6 +307,14 @@ static void netfs_collect_read_results(struct netfs_io_request *rreq)
 			notes |= HIT_PENDING;
 
 		transferred = READ_ONCE(front->transferred);
+		if (unlikely(transferred > front->len)) {
+			/* Ugh...  A subreq overran its allotted length.  It
+			 * may have corrupted the read buffer.
+			 */
+			stream->error = -EIO;
+			stream->failed = true;
+			goto abandon_request;
+		}
 
 		/* If we can collect the next folio from a pending op, do so,
 		 * but we should only do it if we don't otherwise need to wait
@@ -627,6 +635,21 @@ void netfs_read_subreq_terminated(struct netfs_io_subrequest *subreq)
 		break;
 	}
 
+	/* If the subrequest read more than it was supposed to, abort
+	 * the request with EIO as we may have clobbered other parts
+	 * of the buffer that are already read.
+	 */
+	if (subreq->transferred > subreq->len) {
+		trace_netfs_sreq(subreq, netfs_sreq_trace_too_much);
+		__set_bit(NETFS_SREQ_FAILED, &subreq->flags);
+		__clear_bit(NETFS_SREQ_NEED_RETRY, &subreq->flags);
+		subreq->error = -EIO;
+		trace_netfs_failure(rreq, subreq, subreq->error, netfs_fail_read);
+		trace_netfs_rreq(rreq, netfs_rreq_trace_set_pause);
+		set_bit(NETFS_RREQ_PAUSE, &rreq->flags);
+		goto skip_error_checks;
+	}
+
 	/* Deal with retry requests, short reads and errors.  If we retry
 	 * but don't make progress, we abandon the attempt.
 	 */
diff --git a/include/trace/events/netfs.h b/include/trace/events/netfs.h
index 071d20e80f13..723cb7315308 100644
--- a/include/trace/events/netfs.h
+++ b/include/trace/events/netfs.h
@@ -132,6 +132,7 @@
 	EM(netfs_sreq_trace_submit,		"SUBMT")	\
 	EM(netfs_sreq_trace_superfluous,	"SPRFL")	\
 	EM(netfs_sreq_trace_terminated,		"TERM ")	\
+	EM(netfs_sreq_trace_too_much,		"!TOOM")	\
 	EM(netfs_sreq_trace_wait_for,		"_WAIT")	\
 	EM(netfs_sreq_trace_write,		"WRITE")	\
 	EM(netfs_sreq_trace_write_skip,		"SKIP ")	\